1. Field of the Invention
The present invention relates to the preparation of granulated materials, and more particularly to the preparation of granulated perborate salts, such as anhydrous sodium perborate, as well as to the granules thus obtained.
2. Description of the Prior Art
Perborate salts such as sodium perborate monohydrate, and sodium perborate anhydrous have enjoyed broad use in the preparation of a variety of cleansing compositions, and particularly as ingredients in denture cleansers. The perborate salts are popular because of their elevated active oxygen content and temperature stability.
Generally, anhydrous sodium perborate, of the grade and texture utilized in the preparation of denture cleansing tablets, is a fluffy material of low specific weight. These properties impede the rapid and successful preparation of compressed cleanser tablets, and the tablets so prepared frequently fracture or disintegrate. Previous efforts to increase the specific weight of anhydrous sodium perborate, to make it more compressible and thereby a more manageable tableting ingredient, have failed, and prior art efforts in this regard have relied primarily upon the addition to the entire cleansing composition of one or more tableting aids such as talc, sodium benzoate, and the like. These ingredients, however, have certain drawbacks, particularly in the instance where the tablet activity is a function of its speed of disintegration in a liquid such as water. In such instance, the tableting aids tend to prolong the disintegration time of the tablet, with the result that the activity of the tablet is delayed, and the tablet is less attractive to the consumer.
A process is disclosed in U.S. Pat. No. 4,115,519 to Brichard et al., for the manufacture of sodium perborate monohydrate, that purportedly results in the preparation of granules of the monohydrate possessing the desired particle size, specific weight, abrasion resistance and flowability sought for use in connection with the compaction of dental cleanser tablets. The technique disclosed by the patent, however, is complex and costly, and requires specialized apparatus to conduct a fluidized bed particle formation in contact with hydrogen peroxide. The patentees refer to prior art processes for the formation of the monohydrate salt, and indicate that those processes, as well, are complex and expensive, and frequently yield particles that are unsuitable for the present applications.
U.S. Pat. No. 3,340,152, to Hotko, discloses that polyfluorocarbons may be utilized in the manufacture of tablets, as lubricants, and in amounts by weight of the tableting composition, ranging from about 1% to about 15% by weight, to supplant such known lubricants as magnesium stearate, sodium lauryl sulfate, polyethylene glycols and the like. Hotko suggests that the fluoropolymer may be added directly to the tableting mixture, in its capacity and amount as a lubricant, and purportedly has a favorable effect on the tablet-forming process. There is no disclosure in Hotko that the fluoropolymers would serve as agglomeration or compaction aids, to facilitate the preparation of granulated materials of increased and improved specific weight.
A need therefore exists for a method and associated granular product, that provides the perborate salts, and in particular, anhydrous sodium perborate, in a form that is easily and efficiently compressed in combination with other ingredients of a tablet-forming cleanser composition.